Granulocyte antigens play an important role in cell function including adhesion, cell activation, and binding of immunoglobulins. The purpose of these studies is to better define the molecular basis of variations in neutrophil antigens and their role in neutrophil function. Neutrophil-specific antigen HNA-2a (NB1) has been localized to NB1 glycoprotein (gp) which is expressed on subpopulations of neutrophils. The gene encoding the NB1 gp was recently sequenced and called NB1. Another group described a gene called PRV-1 that is highly homologous to NB1. We found that NB1 and PRV-1 are alleles of the same gene, CD177, and showed that this gene is located on chromosome 19q13.31. In addition, we found that a pseudo gene homologous to exons 4 through 9 of CD177 was located on adjacent to CD177 on chromosome 19q13.31. The most common polymorphisms of CD177 was found to be a G to C change at bp42. Recently, CD177 has been found to be over expressed in neutrophils from patients with polycythemia vera. We are also investing the investigate the molecular basis for the variable expression of CD177 and the expression of CD177 in patients with myeloproliferative diseases. Durning pregnancy or following transfusion people often make antibodies directed to antigens expressed by neutrophils. When blood donors produce these antibodies to neutrophil specific antigens the inadvertant transfusion of these antibodies has been associated with transfusion reactions. However, not all patients given blood products with neutrophil antibodies experience a transfusion reaction and the type of transfusion reaction varies among individuals. Studies are underway to investigate the role of antibodies directed to leukocytes in transfusion reactions.